Turbine power plant control with an on-line optimization control

ABSTRACT

Means for speeding up the assessment and optimization process for a turbine engine control including a factor that estimates the change in steady state fuel flow required to maintain the desired thrust level.

1 1| Unite States atent 11 1 1111 3,758,764

Harner Sept. 11, 1973 [54] TURBINE POWER PLANT CONTROL WITH 3,096,4717/1963 Taylor 235/1501 X AN ONJJNE OPTIMIZATION CONTROL 3,377,848 4/1968Marvin 60/3928 R X l K I H w d C 3,472,027 10/1969 Snow et al1 60/3928 RX t 't [75] nven or erml arner, m sor onn OTHER PUBLICATIONS W3]Asslgnee: Un'ted A'rcrafl Carpomhon East Self-Organizing Control ofAdvanced Turbine En- Hartford Conngines by Barron et al., 8-1969,Technical Abstract 22 i Oct. 29 1970 Bulletin 60-20, Oct. 15, 1969, No.AD-857616, Na-

tional Technical Information Service. [21] Appl. No.1 85,046

Primary Examiner-Eugene G. Botz 52 us. 01 235/1502, 235/1501, 60/3928Alwr'IeyNOrman Friedland [51] Int. Cl G05b 13/02, F02 F02c [58] Field ofSearch ..235/151.1, 151.3, ABSTRACT 235/1502; 60/3928, 242, 233 Meansfor speeding up the assessment and optimization process for a turbineengine control including a factor [56] References Cited that estimatesthe change in steady state fuel flow re- UNITED STATES PATENTS quired tomaintain the desired thrust level.

2,842,108 7/1958 Sanders 235/1501 X 5 Claims, 3 Drawing Figures PATENTEBSEP] 1 I973 SHEU 1 (If 3 PATENTEDS 1 i915 3.758.764

SHEET 3 BF 3 baa 6 amwqaorrya d aarpyaawoy TURBINE POWER PLANT CONTROLWITH AN ON-LINE OPTIMIZATION CONTROL The invention herein described wasmade in the course of or under a contract or subcontract thereunder withthe Department of the Air Force.

BACKGROUND OF THE INVENTION This invention relates to a control systemfor turbotype of power plant of the type having at least one or bothvariable turbine inlet nozzles and variable area exhaust nozzles, incombination with a self-organizing control system utilized foroptimizing thrust specific fuel consumption at all thrust conditions byproducing maximum cycle and propulsive efficiency.

The turbine type of power plant in current use today is generally offixed geometry and that the only variable that affects control,performance and power of the engine is the quantity of fuel fed to theburner section. It is customary to provide in such a fuel control,sensors that monitor certain power plant operating conditions so as toschedule fuel flow to produce a desired thrust or power plant operatingcondition. Such heretofore known fuel controls serve to schedule thesteady state and acceleration and/or-deceleration operating conditionsin order to prevent overtemperature, surge, rich and lean blowouts.These controls are designed with a predetermined schedule reflecting theengines performance characteristics. While such schedules attempt tooptimize fuel consumption and engine operating efficiency, theynonetheless are subjected to the preascertained performance criteriawhich may deteriorate after continuous usage of the power plant.

Since the advent of high performance turbine type of power plants whichnot only include the adjustable fuel flow but also include variableengine geometry such as variable turbine nozzles and variable exhaustnozzles, the problem of designing a fuel control that will achieveoptimum fuel consumption isobviously more complex. To this end, thisinvention relates to a system directed at achieving optimum thrustspecific fuel consumption (TSFC) by controlling the thrust of theturbine power plant in a deterministic manner by adjusting fuel flow andto optimize TSFC in an adaptive" manner by adjusting engine geometry.While the term adaptive in the context of this specification isillustrated by the selforganizing control system described in U.S. Pat.No. 3,460,096 granted to R. L Barron on Aug. 5, 1969 it is not limitedthereto. In this typeof system, power plant variables havecharacteristics which may be unknown and difficult to predict arecontinuously monitored during transient and steady state operatingconditions to adjust fuel flow, turbine nozzle area, and exhaust nozzlearea to experimentally calculate the performance of the power plant inorder to zero in on the optimum TSFC. The self-organizing control systemis utilized solely to control the geometry of the turbine power plant byproviding a search for system parameter values during quasi steady stateconditions for optimizing the engine's performance. The fundamentaldesign of the controller incorporates the probability state variablesearch algorithm which is suitable for simultaneous adjustments inmultiple parameters. The self-organizing control system includes aperformance assessment unit which in part employs differentiation ordifference techniques and logic for computing a binary performance valuesignal (V) which indicates if trends are favorable or adverse.

In the preferred embodiment of the self-organizing control system, aperformance assessment unit receives measures of fuel flow and thrustchanges to compute if TSFC is increasing or decreasing so as to make thedetermination independently of any thrust transients resulting frompower lever changes or environmental factors.

Correlation logic units of the self-organizing controller implement theparameter search under the guidance of the performance assessment unitfor optimum engine areas or other parameter values being optimized. Thebasic design of the crrelation logic correlation incorporates theprobability state variable (PSV) search algorithm. This algorithm issuited for simultaneous adjustment for two or more parameters, providingthe performance assessment unit has capabilities for resolving the verysmall performance differences which are obtained in the proximity of theoptimum in the space of parameters. The correlation logic units areemployed in alternating adjustments of the parameters for which theproblem of performance resolution is greatly alleviated. In thisinstance a two state search is utilized in which simultaneous parameteradjustments are first made to bring the system close to its optimumstate in the minimum of time after which alternating adjustments aremade to effect fine tuning. The correlation logic units receive thevalue signal V calculated in the performance assessment unit andcorrelates this signal with information as to the polarity of theimmediate past search experiment. In the PSV search mode, a correlationsignal biases a centered (zero-mean) random variable, the polarity ofthe resulting biased random variable being detected to find the sense ofthe next experiment, and all correlation logic units generate outputchanges simultaneously at a presecribed frequency or asynchronously. Inthe alternating search mode, the correlation signal is detected withoutgoing through summation with a random variable and only one correlationlogic unit generates an output change at a time, with each correlationlogic unit taking its turn in a prescribed manner.

In order to evaluate whether a given change in an engine variable willincrease or decrease T.S.F.C. usually requires that the transientresulting from the disturbance be allowed to decay to essentially steadystate conditions before an accurate assessment can be made. If thechange in thrust and fuel flow are evaluated before the system hasreached an equilibrium condition, erroneous conclusions can be reached.

By including a weighting term in the assessment which accounts for thefact that any engine rotor acceleration which is present at the time theassessment is made will eventually be converted to an additional thrustincrement, it is possible to speed up to the assessment and optimizationprocess. The estimation of the change in steady state fuel flow requiredto maintain the desired thrust level as engine variables are manipulatedcan therefore be written as AW,,,,= Aw, (TSFC) AF, x AN SUMMARY or THEINVENTION The primary object of this invention is to provide an improvedself-organizing control system.

Another object of this invention is to provide for a jet engine controlsystem having a self-organizing control means for more accuratelyassessing T.S.F.C. by evaluating fuel flow requirements during transientconditions.

A still further object of this invention is to provide means to maintainthe desired thrust level in an SOC fuel control by controlling inaccordance with the expression AW, AW (TSFC) AF" -1 AN Other featuresand advantages will be apparent from the specification and claims andfrom the accompanying drawings which illustrate an embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram of thecontrol system for turbine type power plant showing the preferredembodiment of this invention.

FIG. 2 is a graphical illustration defining a typical curve showing thesurge and temperature limit for variable turbine nozzle areas.

FIG. 3 is a graph illustrating a typical compressor map.

DESCRIPTION OF THE PREFERRED EMBODIMENT As used herein the Definition ofSymbols are as follows:

A turbine nozzle area A N nominal turbine nozzle area A desired turbinenozzle area A J exhaust nozzle area A J REF desired exhuast nozzle areaC? specific heat of gases k ratio of specific heats K change in exhaustnozzle area per unit output from SOC correlation logic unit K change inturbine nozzle area per unit output from SOC correlation logic unit Kinferred thrust control derivative gain K inferred thrust controlintegral gain K inferred thrust control proportional gain M aircraftMach number N rotor rpm N time rate of change of rotor rpm Pam ambientpressure P compressor inlet pressure P compressor discharge pressure Pturbine inlet pressure P, turbine discharge pressure q, heating value offuel T, compressor inlet temperature T, compressor discharge temperature'I,, turbine inlet temperature 'I, turbine discharge temperature Wcompressor airflow W,= main engine fuel flow W, desired main engine fuelflow W, gas flow W, W, v, burner efficiency l1 compressor efficiency11,. exhaust nozzle adiabatic expansion efficiency v, turbine efficiency0, ratio of compressor inlet temperature to standard day temperature Fgross engine thrust F net engine thrust J mechanical equivalent of heat3 acceleration due to gravity f, f,, f function of parameters A T timeinterval for updating SOC control outputs While in the heretofore knownturbine type of power plant the problem of measuring the actual thrustis difficult, the problem is more complicated in the advanced type ofengines where the engine geometry is varied. Unlike engines where thegeometry is fixed measurement of compressor speed, for example, would bemore indicative of thrust than would otherwise be in this type ofadvanced engine. To this end, the present invention utilizes acalculated inferred thrust by computing certain engine operatingparameters.

To lend clarity to the understanding of this invention, the presentportion of the disclosure is directed to a simplified calculation forobtaining an inferred thrust reference signal (all symbols are definedhereinabove).

A reasonable expression for gross thrust of a turbojet with variableturbine nozzle area is given by:

Gas flow, Wg, can be expressed as a function of the conditions enteringthe turbine as follows:

g s s/V s)f( 1/ s) where f (P-,/P relates the turbine flow parameter toturbine pressure ratio.

Since it is impossible to get a reasonable measurement of T Wg can alsobe expressed in terms of the pressure and temperature downstream of theturbine,

( W8 (A5 P7/ V T1) 1 r/ 5) where Substituting equation 3 into 1 yields 85 7f1( 7/ P5) 2 7" plgl u1||/ 7) x-nm 1/2 or, in its expanded form g= s1 V2 1 l p/g am/ 7) f( 1/ t) (Pm) {1 v1 11 (P,/P. """"l}" where:

1' f( lh v/ s) f(P-,/P,) turbine nozzle flow parameter In summary thejet engine thrust will be inferred from the measurement of A P,, (IE/Pand (P,,,,,/P,) as follows:

As noted from FIG. 1, the power lever signal 10 is compared with thethrust inference calculated signal 12 in a suitable electronic summer 14for producing an error signal indicative of the difierence between thedesired and inferred thrust values which signal is then sent through aproportional plus integral plus derivative controller utilized tooperate the system in the following manner.

The signal generated by the proportional plus integral plus derivativecontroller, i.e., fuel flow reference (W is transmitted to the fuelcontrol 16 which may take the form of any suitable fuel metering valveto adjust fuel flow metered to the engine so as to provide the thrustnecessary to minimize the error signal.

So as to prevent overtemperature and surge during acceleration, it iscontemplated to limit the fuel flow rate by calculating the limits andadjust the W, signal accordingly. A better understanding of the limitsnecessary in this embodiment to prevent surge and maximum turbine inlettemperature can be had by referring to FIG. 2. FIG. 2 defines the surgeand temepra ture limiting W,/P characteristics for an engine withvariable turbine nozzle area. The temperature limiting curves 17 are fora 60 F compressor inlet temperature and 2,300 R turbine inlettemperature and the surge limits are shown as curves 19, being plottedfor percentage of corrected compressor speed (N/ V While a rigorousmathematical computation would be necessary to show that surge andtemperature can be ascertained by combining W,/P, m N/ {T and A ascontrol parameters, as will be obvious to one skilled in this art, thefollowing computations will show the validity of the use of theseparameters.

For choked turbine nozzles the following equation can be written Also,it is known that Therefore, by rearrangement we can write a1/ 2v T2( W.P2

Since (I W;W,,) k,, and P /P are essentially constant, it can be seenthat lines of constant (11A,)

'I,,/T, can be super-imposed upon the compressor From the compressorequation the following can be defined Substituting equation 5 intoequation 4a and rearranging Substitution of equation 6 into 3 andsolving for w,/P, Jr, yields Since k (P /P C (1 W IW 1/ b, and q are allnearly constant, it can be seen that W,/l T is uniquely defined for eachpoint on the compressor map (see FIG. 3) provided A is known. Fromequation 7 and the compressor map it is then possible to calculate W/P,FT along the surge line for any value of A With a combination ofequation 3 and 7 it is also possible to define the limiting value ofW/P, as a function of A,,, N and T to provide the desired limitingturbine inlet temperature.

FIG. 3 shows locus of constant corrected turbine inlet temperature(i.e., 13/0 for various (A /A and lines of constant W,/P mfor A A,

Obviously, to provide a theoretically correct temperature limit it isnecessary to define that limit as a function of N and T for a giventurbine nozzle area and then provide a biasing function as the areavaries from its nominal value. From the data evaluated to date areasonable temperature limited value of W,/P can be defined from:

( I/ 4) uu (WI/P4) LIM AT you AREA K 5 5 h/ s NOM] As an alternative itis contemplated to calculate for the maximum and minimum turbine areasand adjust for points in between by making a linear interpolationbetween the high and low area values.

The concept of a self-organizing control (SOC) consists of a continuousseries of experiments performed by making small perturbations of theindependent variables to be optimized. The system performance is thenevaluated after each experiment to determine if the overall performancehas been improved or degraded as a result of the perturbation. Thecontrol binary logic is designed to provide a reward (or penalty) binarysignal from the computed improved (or degraded) performance assessment(PA). A reward signal causes the trend of perturbations in the futureexperiments to occur in the same direction that caused the reward. In asimilar manner, a penalty signal causes the trend of perturbations inthe future experiments to occur in the opposite direction. Thecontinuous search for improved performance will result in the enginevariables being adjusted, as required, to achieve the best performance.After having reached the best performance, the experiments will continueto occur but remain in the vicinity of the best performance.

It is obvious that the detailed mechanization of this concept can bedone in various ways with a varying amount of complexity andsophistication.

In the preferred embodiment as can be seen from FIG. 1 and being one ofthe simplest mechanizations perturbs one variable at a time, thendetermine the resulting performance improvement (or degradation). Afterevery variable, in turn, has been perturbed and a performance assessmentfor each has been determined, the sequence is repeated. The direction ofthe perturbation of each variable is determined by the precedingperturbation of that variable and the resulting computed performanceassessment.

In FIG. 1, the PA module 20 is designed to assess thrust specific fuelconsumption, TSFC, where TSFC W,/Thrust. As would be obvious to oneskilled in this art, it is evident that the PA module may be designed toprovide a performance assessment of other parameters. The PA modulereceives signals from A F W,, N and computes a binary signal, SGN V, asfollows:

where A E W,", and N" are the values of AF,,,-,, W,, and N that weresensed one time interval (AT prior to sensing AF W,, N. Rewritingequation 1 and dividing by the term (l puts the equation in the form:

2 Aw,,,,,,= AW, (TSFC) AF, K AN Although a sensed A F is not normallyavailable, a satisfactory substitute may be obtained from sensedaircraft acceleration and known aircraft mass in a conventional manner.During the time interval, A T the sensed A F changes from A F-,,-," toAF Similarly sensed W, changes from W, to W, and N (being theinstantaneous time derivative of sensed N) changes from N i m N. n isevident that a A F-,,-, A F will cause V to increase whereas W, W, willcause V to decrease. The appropriately weighted sum of (A F A F,,,,-,')and (W, W,') will yield a V' 0 when thrust specific fuel consumption,W/F has improved (decreased), whereas V' 0 if the thrust specific fuelconsumption has degraded (increased). It is important to note that ATmust be sufficiently long to permit the engine to be at steady state toobtain an accurate assessment if the V is based only on A F and W, asdescribed above. The minimum permissible A T is predominantly determinedby the engine rotor dynamic lag, such that A T must be at least secondsat lower power. The A T can be significantly reduced if the computationof V is modified to include a weighted value of (N N"). The weightedvalue of (N N) is indicative of the amount of system performance beingused to accelerate or decelerate the engine rotor that will ultimatelyappear as an increment in thrust. Hence, including (N N) in thecomputation of V results in V being equal to the steady state valuebefore steady state conditions are actually achieved.

The synchronizer 24 establishes the time at which the signal, SGN V, istransmitted to each correlation logic unit (CL). The synchronizer inconjunction with the signal, SGN V, determines SGN V and SGN V, bysampling SGN V at the appropriate time.

A correlation logic unit evaluates the preferred direction of the nextperturbation, Ap., based on the past Ap. (i.e. Au") and the resultingSGN V. Ap. is a binary signal indicating the preferred direction of thenext perturbation (+1 means to perturb +1; -1 means to perturb -l Thus,Ap. is the value of Ag. determined in the preceding time interval. Thiscan be mechanized by a simple multiplication of binary signals as shown:

Ag, 1 (SGN V Apf) l -2 2) l a As can be seen in FIG. there are twocorrelation logic units CLl for A, and CL2 for A There is always onecorrelation logic unit for each independent variable in the SOC. Thesynchronizer establishes the time of the next perturbation in Ap.. Aa,and A are perturbed alternately at time intervals of A T The constants,K and K re resented by blank box 26 26, scale the binary signals AIL;and Ap. respectively, to provide the desired perturbation magnitude in AA, and A A The SOC control of A, has provision for alternate controllogic when engine limits have occurred. In particular, when overspeedoccurs, the perturbations in A A, are always toward decreased A, to aidin eliminating overspeed and also permit the control to operate at thedesired thrust and at maximum speed. The perturbations of A, in thisalternate mode have a magnitude of A AJ I The up-down accumulators 2828' collect and store the sum of all perturbations. The first orderlags, included in smoothing filters 30 30' following the updownaccumulators, are optional providing smoothing of the discrete steps inthe up-down accumulator. These signals, A, and A are the reference (orinput) for the A, and A servos 32 34 respectively. The servo actuatorsadjust the engine geometry A, and A, in response to A, and A, in aconventional manner.

A slightly more sophisticated SOC control, being a modification of thepreceding SOC description can search out the best operating conditionsfaster when an SOC control has many independent variables. All theindependent variables are perturbed simultaneously and the computed SGNV is the result of these combined perturbations. The computing mechanismfor the SOC is'not shown here for the sake of clarity, simplicity, andconvenience, but for further details reference should be made to U.S.Pat. No. 3,460,096.

Only the correlation logic units and synchronizer describer previouslyare modified; hence, only the operation of these units will be describedhere. The signal,

SGN V, is continuously transmitted to every correlation logic unit, CL.The synchronizer establishes the time of the next perturbation in theAn. Generally the synchronizer is designed to cause a perturbation fromevery CL to occur simultaneously.

The CL first evaluates the preferred direction of the next perturbation,A based on the past Ap. and SGN V resulting from the simultaneousperturbations (in a manner such as described previously). This signal issmoothed in a filter such as a first order dynamic lag. A noisegenerator in each CL provides a random signal which is added to theoutput signal from this filter. The next perturbation, Au, is in thedirection of the sign of this resulting signal. it can be seen that theAg. from each CL tends to be in the direction yielding improvedperformance in the past several experiments. However, thenon-deterministic manner used in computing each Ap. causes variouscombinations of Ag. perturbations to occur. Each CL will tend towardproviding a A that has provided improved performance in the past severalexperiments. The overall effect is that all independent variables tendto be adjusted simultaneously toward yielding the best performance.

It should be understood that the invention is not limited to theparticular embodiments shown and described herein, but that variouschanges and modifications may be made without departing from the spiritor scope of this novel concept as defined by the following claims. A

I claim:

1. In a self-organizing control system for a turbine type of power planthaving a compressor and variable area mechanisms, said system havingperformance assessment means responsive to power plant operatingparameters for assessing the performance of said power plant,correlation logic means responsive to the performance assessment meansfor adjusting the perfonnance by varying said variable area mechanism ina phase relationship, said performance assessment means including therate of change of said compressor so that the performance assessment ismade during a transient condition of the power plant.

2. in a self-organizing control system as claimed in claim 1 whereinsaid adjusting means includes the control of said turbine type of powerplant, the power assessment means for assessing the performance includesan N term and the estimated change in fuel flow resulting after atransient at a given thrust level is given by the equation:

where K a constant TSF C thrust specific fuel consumption F, net enginethrust A rate of change of speed 3. A fuel control for a turbine type ofpower plant having a compressor and variable area geometry incombination with a self-organizing control having means for assessingthe performance of said power plant, fuel metering means having itsindependent control, means for ascertaining the net thrust of said powerplant, said self-organizing control including power assessment meansresponsive to said fuel metering means, said net thrust ascertainingmeans and the rate of change of the speed of said compressor whereinsaid rate of change of the speed of said compressor serves to speed upthe response time of said power assessment means.

4. A fuel control as claimed in claim 3 wherein said variable areageometry includes the exhaust nozzles and turbine stator vanes of thepower plant, adjusting means for positioning said stator vanes andexhaust nozzle, said performance assessment means includes a N term andthe estimated change in fuel flow after a transient at a given thrustlevel is given by the equation:

A N =Aw, (TSFC) AF, K A A;

(:Btimalc where K a constant W, fuel flow TSFC thrust specific fuelconsumption I? net engine thrust N rate of change of speed 5. Aself-organizing control as claimed in claim 3 including a correlationlogic unit responsive to said performance assessment means fordetermining the phase relationship of the signal generated by saidperformance assessment means and a synchronizer establishing the timeinterval of said correlation logic unit for performing experiments onthe performance of said power plant by perturbations of said variablearea geometry.

UNITED STATES PATENT QFFICE CETIFICATE o CECTWN Patent No. 3,758,764Dated September 11, L223 Durante- (3) Kermit I. Harner It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 12, "crrelation" should read "correlation-- Column 3,line 61, should read 7 b Column 3, line 62, "V should read 7 c Column 3,line 63, "V' h ld d "q Column 3, line 64, should read "*7 t Column 4,line 51, after "(k-l)/k" delere. 1

Column 4, line 52 "l V should read --1 I T Column 5 line 35, a (l W /Wshould read I W (1 w /w Column 5, line 64, T should read (T T Column 5,.line 64, V should read 3) b Column 5, near line 67, "V should read 7 bColumn 6, line 38, I Vb" should read 7 b g.3 UNITED STATES PATENT GFFICECETIHCAT 6F QQECTWN patent 3,758,764 Dated September 1]., 1973 'Inventg(s Kermit I, Harner It is certified that error eppears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 7, line 60, "V' 0" should read V" O Signed and sealed this 26thday of March 1974.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. C. MARSHALL DANN Attesting Officer Commissionerof Patents Notice of Adverse Decision in Interference In InterferenceNo. 100,445, involving Patent No. 3,758,764, I. Harner, TUR- BINE POWERPLANT CONTROL WITH AN ON-LINE OPTIMIZATION, final judgment adverse tothe patentee was rendered May 5, 1982, as to claims 1 and 3.

[Official Gazette August I 7, 1982.]

1. In a self-organizing control system for a turbine type of power planthaving a compressor and variable area mechanisms, said system havingperformance assessment means responsive to power plant operatingparameters for assessing the performance of said power plant,correlation logic means responsive to the performance assessment meansfor adjusting the performance by varying said variable area mechanism ina phase relationship, said performance assessment means including therate of change of said compressor so that the performance assessment ismade during a transient condition of the power plant.
 2. In aself-organizing control system as claimed in claim 1 wherein saidadjusting means includes the control of said turbine type of powerplant, the power assessment means for assessing the performance includesan N term and the estimated change in fuel flow resulting after atransient at a given thrust level is given by the equation: Delta WfDelta Wf - (TSFC) Delta Fn -K Delta N where K a constant Wf fuel flowTSFC thrust specific fuel consumption Fn net engine thrust N rate ofchange of speed
 3. A fuel control for a turbine type of power planthaving a compressor and variable area geometry in combination with aself-organizing control having means for assessing the performance ofsaid power plant, fuel metering means having its independent control,means for ascertaining the net thrust of said power plant, saidself-organizing control including power assessment means responsive tosaid fuel metering means, said net thrust ascertaining means and therate of change of the speed of said compressor wherein said rate ofchange of the speed of said compressor serves to speed up the responsetime of said power assessment means.
 4. A fuel control as claimed inclaim 3 wherein said variable area geometry includes the exhaust nozzlesand turbine stator vanes of the power plant, adjusting means forpositioning said stator vanes and exhaust nozzle, said performanceassessment means includes a N term and the estimated change in fuel flowafter a transient at a given thrust level is given by the equation:Delta Wf Delta Wf - (TSFC) Delta Fn - K Delta N where K a constant Wffuel flow TSFC thrust specific fuel consumption Fn net engine thrust Nrate of change of speed
 5. A self-organizinG control as claimed in claim3 including a correlation logic unit responsive to said performanceassessment means for determining the phase relationship of the signalgenerated by said performance assessment means and a synchronizerestablishing the time interval of said correlation logic unit forperforming experiments on the performance of said power plant byperturbations of said variable area geometry.